Through the years zoologists have devised various methods of categorizing animals in to their varied species types. While the prominent zoologists have contributed their own theory and methods of classification of animals, yet they all follow the basic theory of two broad based categories, under which there are then the sub-categories.
All animals are broadly classified as :
- Vertebrates :
- Invertebrates :
The invertebrates, broadly speaking, are all those animals that do not have a backbone or spinal column. This is further classified into the following types :
Protozoa - (phyla: protozoa) :
These are the single-celled simple animals that are largely extremely tiny or microscopic, implying that they can be seen only through the lens of a microscope. Amongst the varied types of protozoa are amoeba and flagellates.
Echinoderms - (phyla: Echindermata) :
Theses are basically the marine animals existing in the depths of the ocean. Characteristically they have spines or arms that spread out from the center of their body. Their organs and mouth for feeding exist in the central body. Echinoderms include the starfish and sea urchins.
Annelids - (phyla: Annelida) :
The bodies of these animals are divided into varied. These creatures have properly internal organs. There are presently as many as 9,000 known species of Annelids, which includes worms and leeches.
Mollusks: (phyla: Mollusca) :
these are known to be amongst the first inhabitants of planet Earth. These creatures are normally characterized by the hard shells that protect them. Mollusks include those that live on land such as snails and slugs; as well as those that inhabit the water such as oysters, mussels, clams, squids and octopuses.
Arthropods - (phyla: Arthropoda):
This class of animals constitutes over 75 per cent of the animal species of the world. These include insects (The largest group of arthropods with over 800,000 varied types), crustaceans (crab, lobster and barnacle) and arachnids (spider, scorpions, ticks and mites).
The vertebrates are animals that have a skeleton within, which is made of bones. These include the varied sub-classes of vertebrate animals :
Fish :
There are more than 20,000 varied species of fish; and the earliest fish fossils found dates back to over 400 million years.
Amphibians :
These animals lay their eggs in water. For instance, the frogs lay their eggs in water that then take the form of fish-like tadpoles.
Reptiles :
These animals are normally referred to as cold-blooded as they are able to control their own body temperature. They can live on land as well as in water and use their lungs and skin accordingly. Reptiles include animals such as lizards, snakes, crocodiles and alligators, amongst others.
Birds :
It is said that the first bird appeared over 150 million years ago and now inhabit ever part of the world. There are over 8,000 known species of birds.
Mammals :
These animals have varied unique characteristics that distinguish them from other animals. Most of them have hair or fur that covers their body. These animals give birth to fully formed babies and the females have mammary glands to feed their young ones. Mammals include the primates (humans, monkeys, baboons, orangutans, chimpanzees and gorillas); marsupials (kangaroos, koala bears and wombat); rodents (squirrels, mice, porcupines); whales; dolphins; and seals (seals, seal lions and walrus).